Urate Transporter 1 Can Be a Therapeutic Target Molecule for Chronic Kidney Disease and Diabetic Kidney Disease: A Retrospective Longitudinal Study

Chronic kidney disease (CKD) is a major global health problem for which there are no curative drug treatments. Hyperuricemia is one of risk factors for CKD. The evidence on effects of uric acid (UA)-lowering treatments on the progression of CKD was very limited and previous meta-analyses used only trials which primarily used xanthin oxidase (XO) inhibitors because the reports on fulminant hepatitis due to benzbromarone kept us from using uricosuric agents for hyperuricemia patients. Dotinurad, a novel selective urate reabsorption inhibitor for the treatment of hyperuricemia, reduces serum UA levels by selectively inhibiting urate transporter 1 (URAT1). We retrospectively picked up patients who had taken dotinurad from June 2018 to August 2021 and compared metabolic parameters at baseline with the data at 3 and 6 months after the start of dotinurad. We found 84 patients, and approximately 74% of patients were complicated with CKD. After the start of dotinurad, improvements in serum lipids, systolic blood pressure, body weight, and albuminuria, in addition to reduction in serum UA, were observed. Dotinurad increased urinary UA excretion, and was effective to reduce serum UA in patients with both UA underexcretion type and renal UA overload type. Furthermore, urinary UA excretion was significantly and negatively correlated with serum creatine levels at baseline and at 6 months after the start of dotinurad, and the change in urinary UA excretion after 3 months was significantly and negatively correlated with change in serum creatine levels. The property of dotinurad, which selectively inhibits URAT1, but not other UA transporters, such as ATP-binding cassette, subfamily G, and 2 (ABCG2), which ABCG2 is a UA and uremic toxin exporter, may be beneficially associated with pathology of CKD. URAT1 can be a therapeutic target molecule for CKD and DKD.


Introduction
Chronic kidney disease (CKD) is a major global health problem for which there are no curative drug treatments. Lifestyle-related diseases, such as obesity, hypertension, diabetes, and dyslipidemia, are currently important risk factors for CKD [1]. Evidence supports a pathophysiological role for overactivation of the mineralocorticoid receptor in cardiorenal diseases, including CKD and diabetes, through inflammation and fibrosis that lead to progressive kidney and cardiovascular dysfunction [2]. A nonsteroidal, selective mineralocorticoid receptor antagonist (MRA), finerenone, had more potent anti-inflammatory and anti-fibrotic effects than steroidal mineralocorticoid receptor antagonists in preclinical models [3]. Very recently, the treatment with a selective MRA resulted in lower risks of CKD progression than placebo in patients with CKD and type 2 diabetes [4]. The treatments for diabetes and obesity, such as sodium-glucose co-transporter 2 (SGLT2) inhibitors and glucagon-like peptide-1 receptor agonists (GLP-1RA), are emerging as promising treatment options in CKD and diabetic kidney disease (DKD) [5][6][7][8][9][10][11]. The therapeutic intervention for the Japanese Society of Hypertension, Japan Atherosclerosis Society; Japanese Society of Gout and Uric and Nucleic Acids, we defined type 2 diabetes as taking anti-diabetic drugs and/or HbA1c > 6.5%; hypertension as taking anti-hypertensive drugs and/or systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg; dyslipidemia as taking anti-hyperlipidemic drugs and/or low-density lipoprotein-cholesterol (LDL-C) ≥ 140 mg/dL and/or triglyceride (TG) ≥ 150 mg/dL and/or triglyceride highdensity lipoprotein-cholesterol (HDL-C) < 40 mg/dL; hyperuricemia as taking uric acid (UA) lowering drugs and/or serum UA ≥ 7.0 mg/dL, respectively. According to the diagnostic criteria by the Japanese Society of Nephrology, CKD was defined as reduced eGFR (eGFR < 60 mL/min/1.73 m 2 ) or proteinuria including albuminuria (urinary albumin/creatinine [UACR] ≥ 30).

Laboratory Measurements
Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gammaglutamyl transferase (GGT) were measured by a modified Japan Society of Clinical Chemistry (JSCC) reference method. Serum albumin was measured by the modified bromocresol purple (BCP) method. Serum UA was measured by uricase peroxidase method. Plasma glucose was the hexokinase UV method. Hemoglobin A1c (HbA1c) was measured by automated enzyme-linked immunosorbent assays (TOSOH, Tokyo, Japan). Serum creatinine, TG, HDL-C, and LDL-C were determined enzymatically. The eGFR was calculated by using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula. To understand urinary excretion of UA, we measured urinary UA/creatinine.

Adjustment of Concurrent Treatments for Lifestyle-Related Diseases except for Hyperuricemia
Anti-hypertensive drugs, such as angiotensin receptor blockers (ARB), and antihyperlipidemic drugs, such as statin and SGLT2 inhibitors [9], may affect metabolic parameters, such as blood pressure, serum lipids, and body weight. Therefore, we analyzed the effects of dotinurad on metabolic parameters by dividing into patients with and without anti-hypertensive drugs (ARB and calcium channel blockers), and by dividing into patients with and without anti-hyperlipidemic drugs (statin, pemafibrate, and ezetimibe), and by dividing into patients with and without SGLT2 inhibitors. Furthermore, we studied the effect of dotinurad in patients who had not taken anti-hypertensive and anti-hyperlipidemic drugs and SGLT2 inhibitors.

Statistical Analysis
Statistical analyses were performed by using SPSS version 23 (IBM Co., Ltd., Chicago, IL, USA). All values are expressed as the mean ± standard deviation, except for sex. The paired t-test was used to statistically analyze comparison in metabolic parameters between before and after the start of dotinurad. Correlations between changes in two parameters were statistically analyzed by the Spearman's correlation (non-parametric). p value of <0.05 and <0.1 was considered to be statistically significant, and to have tendency, respectively.

Baseline Characteristics of Patients Studied
We found 84 patients, and baseline characteristics for patients who had taken dotinurad were shown in Table 1. Dotinurad was prescribed to patients with asymptomatic hyperuricemia. The mean BMI was over 27 kg/m 2 , indicating that our study included a relatively large number of overweight patients. Almost 60% of patients had type 2 diabetes, hypertension, and dyslipidemia. Very high-percentage (approximately 74%) of patients were complicated with CKD. Thirty-five patients had not used UA-lowering drugs, and forty-nine patients had undergone the switching from XO inhibitors, such as febuxostat, topiroxostat, and allopurinol, to dotinurad. A half of patients had taken daily 0.5 mg of dotinurad, and 44% of patients had taken daily 1.0 mg of dotinurad.

Concurrent Treatments for Hypertension, Dyslipidemia and Type 2 Diabetes of Patients Studied
Treatments for hypertension, dyslipidemia, and type 2 diabetes at baseline were shown in Table 2. Forty-five percentage of patients had taken ARB and statins, and onethird of patients had taken SGLT2 inhibitors. Such treatments did not change during the study period. Changes in metabolic parameters after the start of dotinurad were shown in Table 3. Body weight, blood pressures, transaminase, glucose, and lipid metabolism did not show any changes. Serum UA did not show a significant change at 3 months after the start of dotinurad as compared with baseline; however, serum UA significantly decreased after 6 months. Interestingly, UACR tended to decrease at 6 months after the start of dotinurad. Changes in metabolic parameters after the start of dotinurad in patients who had not used UA-lowering drugs were shown in Table 4. Body weight, blood pressures, transaminases, and glucose metabolism did not show any changes. Serum LDL-C significantly decreased and non-HDL-C tended to decrease at 3 months after the start of dotinurad as compared with baseline. Serum UA significantly decreased at both 3 and 6 months after the start of dotinurad. UACR tended to decrease at 6 months after the start of dotinurad.

Changes in Metabolic Parameters after the Start of Dotinurad in Patients Who Switched from XO Inhibitors
Changes in metabolic parameters after the start of dotinurad in in patients who switched from XO inhibitors were shown in Table 5. Body weight tended to decrease at 6 months after the start of dotinurad as compared with baseline. Systolic blood pressure significantly decreased at 3 months after the start of dotinurad as compared with baseline. Transaminases, glucose, and lipid metabolism, eGFR and UACR did not show any changes. Serum UA significantly increased at 3 months after the start of dotinurad as compared with baseline; however, serum UA did not show a significant difference at 6 months after the start of dotinurad.

Changes in Urinary UA/Creatinine after the Start of Dotinurad
Changes in urinary UA/creatine after the start of dotinurad in patients were shown in Figure 1. Urinary UA/creatine significantly increased at both 3 and 6 months after the start of dotinurad as compared with baseline in all patients. Among patients who had not used UA-lowering drugs, urinary UA/creatine tended to increase at 3 months after the start of dotinurad as compared with baseline, however, urinary UA/creatine did not show a significant change after 6 months. In patients who switched from XO inhibitors, urinary UA/creatine significantly increased at both 3 and 6 months after the start of dotinurad as compared with baseline.   Changes in metabolic parameters after the start of dotinurad in patients who had taken anti-hypertensive drugs (ARB and calcium channel blockers) were shown in Table  6. Urinary UA/creatinine significantly increased at 3 and 6 months after the start of dotinurad. Serum UA tended to decrease after 3 months and significantly decreased after

Differences in Effects of Dotinurad on Metabolic Parameters between Patients with and without Anti-Hypertensive Drugs
Changes in metabolic parameters after the start of dotinurad in patients who had taken anti-hypertensive drugs (ARB and calcium channel blockers) were shown in Table 6. Urinary UA/creatinine significantly increased at 3 and 6 months after the start of dotinurad. Serum UA tended to decrease after 3 months and significantly decreased after 6 months. UACR tended to decrease after 6 months.
Changes in metabolic parameters after the start of dotinurad in patients who had not taken anti-hypertensive drugs were shown in Table 7. Urinary UA/creatinine showed a significant increase at both 3 and 6 months after the start of dotinurad. However, serum UA did not show a significant change. Body weight and systolic blood pressure tended to decrease at both 3 and 6 months after the start of dotinurad. Serum TG tended to decrease after 3 months. Serum creatine significantly increased and eGFR significantly decreased after 3 months.  Values show mean ± SD. * p < 0.1, ** p < 0.05 vs. baseline. eGFR, estimated glomerular filtration rate; HDL-C, high-density lipoprotein-cholesterol; LDL-C, low-density lipoprotein-cholesterol; Non-HDL-C, non-high-density lipoprotein-cholesterol; TG, triglyceride, UA, uric acid; UACR, urinary albumin creatinine ratio.

Differences in Effects of Dotinurad on Metabolic Parameters between Patients with and without Anti-Hyperlipidemic Drugs
Changes in metabolic parameters after the start of dotinurad in patients who had taken anti-hyperlipidemic drugs (statin, pemafibrate, and ezetimibe) were shown in Table 8. Urinary UA/creatinine significantly increased at both 3 and 6 months after the start of dotinurad. Serum UA did not show a significant change. Diastolic blood pressure tended to decrease after 3 months. UACR tended to decrease after 6 months. Changes in metabolic parameters after the start of dotinurad in patients who had not taken anti-hyperlipidemic drugs were shown in Table 9. Urinary UA/creatinine showed a significant increase at both 3 and 6 months after the start of dotinurad. Serum UA tended to decrease after 6 months. Body weight tended to decrease at 3 months after the start of dotinurad. Interestingly, HbA1c tended to decrease after 6 months. Values show mean ± SD. * p < 0.1, ** p < 0.05 vs. baseline. eGFR, estimated glomerular filtration rate; HDL-C, high-density lipoprotein-cholesterol; LDL-C, low-density lipoprotein-cholesterol; Non-HDL-C, non-high-density lipoprotein-cholesterol; TG, triglyceride, UA, uric acid; UACR, urinary albumin creatinine ratio.

Differences in Effects of Dotinurad on Metabolic Parameters between Patients with and without SGLT2 Inhibitors
Changes in metabolic parameters after the start of dotinurad in patients who had also taken SGLT2 inhibitors were shown in Table 10. Only urinary UA/creatinine showed a significant increase at 3 months after the start of dotinurad. Serum UA did not show a significant difference. Diastolic blood pressure tended to increase after 6 months. Changes in metabolic parameters after the start of dotinurad in patients who had not taken SGLT2 inhibitors were shown in Table 11. Urinary UA/creatinine showed a significant increase at both 3 and 6 months after the start of dotinurad. Serum UA also showed a significant decrease at both 3 and 6 months after the start of dotinurad. Very interestingly, HbA1c significantly decreased at 6 months after the start of dotinurad. Values show mean ± SD. ** p < 0.05 vs. baseline. eGFR, estimated glomerular filtration rate; HDL-C, high-density lipoprotein-cholesterol; LDL-C, low-density lipoprotein-cholesterol; Non-HDL-C, non-high-density lipoproteincholesterol; SGLT2, sodium-glucose co-transporter 2; TG, triglyceride, UA, uric acid; UACR, urinary albumin creatinine ratio.

Changes in Metabolic Parameters after the Start of Dotinurad in Patients Who Had Not Taken Anti-Hypertensive and Anti-Hyperlipidemic Drugs and SGLT2 Inhibitors
Changes in metabolic parameters after the start of dotinurad in patients who had not taken anti-hypertensive and anti-hyperlipidemic drugs and SGLT2 inhibitors were shown in Table 12. Urinary UA/creatinine showed a significant increase at both 3 and 6 months after the start of dotinurad. Serum UA did not show a significant change. Body weight tended to decrease at 3 months after the start of dotinurad. HbA1c tended to decrease after 6 months. Values show mean ± SD. * p < 0.1, ** p < 0.05 vs. baseline. eGFR, estimated glomerular filtration rate; HDL-C, high-density lipoprotein-cholesterol; LDL-C, low-density lipoprotein-cholesterol; Non-HDL-C, non-high-density lipoprotein-cholesterol; SGLT2, sodium-glucose co-transporter 2; TG, triglyceride, UA, uric acid; UACR, urinary albumin creatinine ratio.

Phenotypes of Hyperuricemia and Effect of Dotinurad on Urinary UA/Creatinine
The proportion of hyperuricemia phenotype in our patients were shown in Figure 2. Among patients whose urinary UA/creatinine were measured, almost 88% patients were UA underexcretion type, and the proportion of patients with renal UA overload type was only 12%. The effect of dotinurad on urinary UA/creatinine and serum UA levels in each hyperuricemia phenotype were shown in Figure 3. In patients with UA underexcretion type, dotinurad significantly increased urinary UA/creatinine at both 3 and 6 months after the start of dotinurad as compared with baseline. However, there were no significant changes in serum UA after the start of dotinurad. In patients with renal UA overload type, there were no significant changes in urinary UA/creatinine after the start of dotinurad. However, dotinurad significantly reduced serum UA at both 3 and 6 months after the start of dotinurad as compared with baseline. The effect of dotinurad on urinary UA/creatinine and serum UA levels in each hyperuricemia phenotype were shown in Figure 3. In patients with UA underexcretion type, dotinurad significantly increased urinary UA/creatinine at both 3 and 6 months after the start of dotinurad as compared with baseline. However, there were no significant changes in serum UA after the start of dotinurad. In patients with renal UA overload type, there were no significant changes in urinary UA/creatinine after the start of dotinurad. However, dotinurad significantly reduced serum UA at both 3 and 6 months after the start of dotinurad as compared with baseline.

Correlations between Urinary UA/Creatinine and Serum Creatinine
Correlations between urinary UA/creatinine and serum creatinine were shown in Figure 4. Urinary UA/creatine was significantly and negatively correlated with serum creatine levels at baseline and at 6 months after the start of dotinurad, and urinary UA/creatine tended to be negatively correlated with serum creatine levels after 3 months. The change in urinary UA/creatine after 3 months was significantly and negatively correlated with change in serum creatine. Correlations between urinary UA/creatinine and serum creatinine were shown in Figure 4. Urinary UA/creatine was significantly and negatively correlated with serum creatine levels at baseline and at 6 months after the start of dotinurad, and urinary UA/creatine tended to be negatively correlated with serum creatine levels after 3 months. The change in urinary UA/creatine after 3 months was significantly and negatively correlated with change in serum creatine.

Correlations between Urinary UA/Creatinine and eGFR
Correlations between urinary UA/creatinine and eGFR were shown in Figure 5. Urinary UA/creatine was significantly and positively correlated with eGFR at baseline and at 6 months after the start of dotinurad, and urinary UA/creatine tended to be positively correlated with eGFR after 3 months. Change in urinary UA/creatine tended to be positively correlated with change in eGFR after 3 months.

Correlations between Urinary UA/Creatinine and eGFR
Correlations between urinary UA/creatinine and eGFR were shown in Figure 5. Urinary UA/creatine was significantly and positively correlated with eGFR at baseline and at 6 months after the start of dotinurad, and urinary UA/creatine tended to be positively correlated with eGFR after 3 months. Change in urinary UA/creatine tended to be positively correlated with change in eGFR after 3 months.

Correlations between Urinary UA/Creatinine and eGFR
Correlations between urinary UA/creatinine and eGFR were shown in Figure 5. Urinary UA/creatine was significantly and positively correlated with eGFR at baseline and at 6 months after the start of dotinurad, and urinary UA/creatine tended to be positively correlated with eGFR after 3 months. Change in urinary UA/creatine tended to be positively correlated with change in eGFR after 3 months.

The Association of Serum UA with Serum Creatinie and eGFR 3.8.1. Correlations between Serum UA and Serum Creatinine
Correlations between serum UA and serum creatinine were shown in Figure 6. Serum UA level was significantly and positively correlated with serum creatine levels at 3 months after the start of dotinurad, and serum UA level tended to be positively correlated with serum creatine level after 6 months. Change in serum UA was significantly and positively correlated with change in serum creatine levels at 3 months after the start of dotinurad, and the change in serum UA tended to be positively correlated with change in serum creatine levels at 6 months after the start of dotinurad.

Correlations between Serum UA and Serum Creatinine
Correlations between serum UA and serum creatinine were shown in Figure 6. Serum UA level was significantly and positively correlated with serum creatine levels at 3 months after the start of dotinurad, and serum UA level tended to be positively correlated with serum creatine level after 6 months. Change in serum UA was significantly and positively correlated with change in serum creatine levels at 3 months after the start of dotinurad, and the change in serum UA tended to be positively correlated with change in serum creatine levels at 6 months after the start of dotinurad.

Correlations between Serum UA and eGFR
Correlations between serum UA and eGFR were shown in Figure 7. Serum UA levels were not correlated with eGFR at any time after the start of dotinurad. Furthermore, change in serum UA levels were not correlated with change in eGFR at both 3 and 6 months after the start of dotinurad.

Correlations between Serum UA and eGFR
Correlations between serum UA and eGFR were shown in Figure 7. Serum UA levels were not correlated with eGFR at any time after the start of dotinurad. Furthermore, change in serum UA levels were not correlated with change in eGFR at both 3 and 6 months after the start of dotinurad.

Discussion
Almost 60% of our patients had type 2 diabetes, and over 70% of patients have CKD; therefore, present study could observe the effect of a novel selective URAT1 inhibitor, dotinurad on metabolic and renal parameters in CKD and DKD patients. In other words, this study may clarify a clinical significance of URAT1 in CKD and DKD. Renal excretion of UA is the major regulator of serum UA concentration [28][29][30]. In humans, reabsorption of UA into the blood plays a crucial role to regulate serum UA. The UA exchange is mediated by various molecules, such as URAT1, glucose transporter 9 (GLUT9), and ABCG2, expressed in renal proximal tubule [31][32][33][34]. Renal UA reabsorption is mainly mediated by URAT1 and GLUT9 [33,35,36]. URAT1 is found in the apical membrane of proximal tubule epithelial cells [37]. In addition, ABCG2 has been identified as a high-capacity UA exporter that mediates renal and/or extra-renal UA excretion [38]. ABCG2 is now known to be involved as well in UA excretion into the intestine [38].
We found that dotinurad improved UACR in addition to serum UA in all patients and patients who had not used UA-lowering drugs. An increase in urinary UA excretion measured by urinary UA/creatine can indicate the inhibitory effect of URAT1 by dotinurad. Dotinurad significantly increased urinary UA/creatine in all patients, especially in patients who switched from XO inhibitors. As almost 88% of our patients were UA underexcretion type, such patients should have been treated by uricosuric agents. As the effect of dotinurad on urinary UA/creatinine in each hyperuricemia phenotype showed, dotinurad significantly increased urinary UA/creatinine in patients with UA underexcretion type. More interesting is the effect of dotinurad on urinary UA/creatinine and serum UA levels in patients with renal UA overload type. In patients with renal UA overload type, there were no significant changes in urinary UA/creatinine by dotinurad. However, dotinurad remarkably reduced serum UA as compared with baseline. On the other hand, in patients with UA underexcretion type, despite significant increase in urinary UA/creatine, the decrease in serum UA levels was modest. This suggests that expression and/or function of URAT1 in patients with UA underexcretion type may be higher than those in patients with renal UA overload type. In short, while the same dose of

Discussion
Almost 60% of our patients had type 2 diabetes, and over 70% of patients have CKD; therefore, present study could observe the effect of a novel selective URAT1 inhibitor, dotinurad on metabolic and renal parameters in CKD and DKD patients. In other words, this study may clarify a clinical significance of URAT1 in CKD and DKD. Renal excretion of UA is the major regulator of serum UA concentration [28][29][30]. In humans, reabsorption of UA into the blood plays a crucial role to regulate serum UA. The UA exchange is mediated by various molecules, such as URAT1, glucose transporter 9 (GLUT9), and ABCG2, expressed in renal proximal tubule [31][32][33][34]. Renal UA reabsorption is mainly mediated by URAT1 and GLUT9 [33,35,36]. URAT1 is found in the apical membrane of proximal tubule epithelial cells [37]. In addition, ABCG2 has been identified as a highcapacity UA exporter that mediates renal and/or extra-renal UA excretion [38]. ABCG2 is now known to be involved as well in UA excretion into the intestine [38].
We found that dotinurad improved UACR in addition to serum UA in all patients and patients who had not used UA-lowering drugs. An increase in urinary UA excretion measured by urinary UA/creatine can indicate the inhibitory effect of URAT1 by dotinurad. Dotinurad significantly increased urinary UA/creatine in all patients, especially in patients who switched from XO inhibitors. As almost 88% of our patients were UA underexcretion type, such patients should have been treated by uricosuric agents. As the effect of dotinurad on urinary UA/creatinine in each hyperuricemia phenotype showed, dotinurad significantly increased urinary UA/creatinine in patients with UA underexcretion type. More interesting is the effect of dotinurad on urinary UA/creatinine and serum UA levels in patients with renal UA overload type. In patients with renal UA overload type, there were no significant changes in urinary UA/creatinine by dotinurad. However, dotinurad remarkably reduced serum UA as compared with baseline. On the other hand, in patients with UA underexcretion type, despite significant increase in urinary UA/creatine, the decrease in serum UA levels was modest. This suggests that expression and/or function of URAT1 in patients with UA underexcretion type may be higher than those in patients with renal UA overload type. In short, while the same dose of dotinurad increases urinary UA excretion, the effect on serum UA levels may be insufficient in patients with UA underexcretion type with higher expressed URAT1; the same dose of dotinurad increases urinary UA excretion, but the effect on serum UA levels may be greater in patients with renal UA overload type with lower expressed URAT1. The increased protein level of URAT1 was observed in obesity/metabolic syndrome model mice [39]. Upon high-purine load, insulin resistance enhances UA reabsorption as manifested by up-regulated URAT1 expression and reduces UA excretion in the Otsuka-Long-Evans-Tokushima Fatty rats [40]. UA underexcretion type may be associated with insulin resistance, which is strongly involved in the development of CKD and DKD. Furthermore, this result suggests that dotinurad is effective to reduce serum UA by using appropriate dose in patients with both UA underexcretion type and renal UA overload type.
We analyzed the correlation of urinary UA/creatinine with the markers for CKD/DKD, such as serum creatinine levels and eGFR. Urinary UA/creatinine was strongly associated with lower serum creatinine levels and higher eGFR, and the increase in urinary UA/creatinine by dotinurad was also associated with an improvement of serum creatinine levels and eGFR. However, the influence of serum UA on serum creatinine levels was weak, and serum UA levels were not associated with eGFR. This suggests that urinary UA excretion may perform a more crucial role in progression of CKD/DKA as compared with serum UA levels.
We found an improvement in serum lipids, such as reduction in LDL-C and non-HDL-C by dotinurad, in patients who had not used UA-lowering drugs. The meta-analysis showed that hyperuricemia increased the likelihood of dyslipidemia, and the pooled OR for the highest UA level vs. the lowest UA level was 1.84 (95%CI, 1.49 to 2.28) [41]. A reduction in serum UA by dotinurad may improve serum lipids. We found an improvement in systolic blood pressure by dotinurad in patients who switched from XO inhibitors. The meta-analysis showed that hyperuricemia was associated with a higher risk of incident hypertension [42]. Adjusted RR was 1.15 (95%CI, 1.06 to 1.26) for a 1 mg/dL increase in serum UA. Another meta-analysis showed that hyperuricemia was associated with an increased risk for incident hypertension (adjusted RR, 1.41; 95%CI, 1.23 to 1.58) [43]. For a 1 mg/dL increase in UA level, the pooled RR for incident hypertension after adjusting for potential confounding was 1.13 (95%CI, 1.06 to 1.20). Hyperuricemia may be also responsible for microvascular damage through stimulation of the renin-angiotensin system (RAS), inhibition of endothelial nitric oxide, and proliferative effects on vascular smooth muscle cells [44]. Did the reduction in serum UA by dotinurad improve systolic blood pressure in our patients who switched from XO inhibitors? The answer is "No". Serum UA significantly increased in patients who switched from XO inhibitors. Why was systolic blood pressure reduced by dotinurad? We also observed a reduction in body weight by dotinurad in patients who switched from XO inhibitors. As one of the causes that SGLT2 inhibitors suppress the progression of CKD, lowering of serum UA by SGLT2 has been suggested [9]. SGLT2 inhibitors increase the concentration of glucose in the proximal tubules, and glucose may compete with UA for apical GLUT9, reducing UA reabsorption [28,45] (Figure 8A). Dotinurad selectively inhibits URAT1 and increases the concentration of UA in the proximal tubules, and UA may compete with glucose for apical GLUT9, reducing glucose reabsorption ( Figure 8B), which may induce an improvement of serum lipids, blood pressure, body weight, and UACR-like SGLT2 inhibitors [9]. In present study, HbA1c significantly decreased in patients who had not taken SGLT2 inhibitors at 6 months after the start of dotinurad, supporting our hypothesis. SGL2 inhibitors improve body weight, dyslipidemia, blood pressure, and UACR [9]. An improvement in body weight, dyslipidemia, blood pressure, and UACR after the start of dotinurad might have been induced by reduced glucose reabsorption by GLUT9. We adjusted confounding variables, such as concurrent medications, for other lifestyle-related diseases except for hyperuricemia because such treatments have an effect on CKD outcome and metabolic parameters. Hyperuricemia was strongly associated with metabolic syndrome [28] and metabolic syndrome, and each factor of metabolic syndrome induce the development and progression of CKD ( Figure 9A). CKD also induces the development and progression of hyperuricemia, dyslipidemia, impaired glucose metabolism, and hypertension [28,46]. We adjusted confounding variables, such as concurrent medications, for other lifestylerelated diseases except for hyperuricemia because such treatments have an effect on CKD outcome and metabolic parameters. Hyperuricemia was strongly associated with metabolic syndrome [28] and metabolic syndrome, and each factor of metabolic syndrome induce the development and progression of CKD ( Figure 9A). CKD also induces the development and progression of hyperuricemia, dyslipidemia, impaired glucose metabolism, and hypertension [28,46].
Anti-hypertensive drugs, such as ARB and calcium channel blockers, have a favorable impact on blood pressure and renal parameters for CKD [47,48] (Figure 9A). Therefore, we analyzed the effects of dotinurad on metabolic parameters by dividing into patients with and without anti-hypertensive drugs. UACR tended to decrease in patients with antihypertensive drugs, suggesting a synergetic effect of dotinurad and anti-hypertensive drugs on UACR. Systolic blood pressure tended to decrease in patients without anti-hypertensive drugs, suggesting that dotinurad reduced blood pressure by possibly a relative inhibition of GLUT9, which was supported by reduction in body weight and serum TG in this population. In this population, serum creatine significantly increased and eGFR significantly decreased after 3 months, which may be due to reduced glomerular hyperfiltration because they lost body weight.
Anti-hyperlipidemic drugs, such as statins, fibrates, and ezetimibe, have beneficial effects on dyslipidemia and CKD [49][50][51][52] (Figure 9A). Diastolic blood pressure and UACR tended to decrease in patients with anti-hyperlipidemic drugs, suggesting a synergetic effect of dotinurad and anti-hypertensive drugs on blood pressure and UACR. Body weight tended to decrease and HbA1c significantly decreased in patients without antihyperlipidemic drugs, which may be also due to a relative inhibition of GLUT9.
SGLT2 inhibitors have beneficial effects on hyperuricemia, dyslipidemia, glucose metabolism, blood pressure, and CKD [9] (Figure 9A). Diastolic blood pressure tended to decrease in patients with SGLT2 inhibitors. Interestingly, HbA1c significantly decreased in patients without SGLT2 inhibitors, which may be also due to a relative inhibition of GLUT9.
We adjusted confounding variables, such as concurrent medications, for other lifestyle-related diseases except for hyperuricemia because such treatments have an effect on CKD outcome and metabolic parameters. Hyperuricemia was strongly associated with metabolic syndrome [28] and metabolic syndrome, and each factor of metabolic syndrome induce the development and progression of CKD ( Figure 9A). CKD also induces the development and progression of hyperuricemia, dyslipidemia, impaired glucose metabolism, and hypertension [28,46]  Anti-hypertensive drugs, such as ARB and calcium channel blockers, have a favorable impact on blood pressure and renal parameters for CKD [47,48] (Figure 9A). Therefore, we analyzed the effects of dotinurad on metabolic parameters by dividing into patients with and without anti-hypertensive drugs. UACR tended to decrease in patients with antihypertensive drugs, suggesting a synergetic effect of dotinurad and anti-hypertensive drugs on UACR. Systolic blood pressure tended to decrease in patients without anti-hypertensive drugs, suggesting that dotinurad reduced blood pressure by possibly a relative inhibition of GLUT9, which was supported by reduction in body weight and serum TG in this population. In this population, serum creatine significantly increased and eGFR sig- Body weight, HbA1c tended to decrease and eGFR tended to increase in patients who had not taken anti-hypertensive and anti-hyperlipidemic drugs, and SGLT2 inhibitors, supporting a significance of a relative inhibition of GLUT-9 by dotinurad for an improvement of metabolic and renal parameters.
The summery of effects of dotinurad with and without concurrent medications for other lifestyle-related diseases except for hyperuricemia were shown in Figure 9B. An improvement of UACR seems to be due to a synergetic effect of dotinurad and antihypertensive, and anti-hyperlipidemic drugs. An improvement of body weight, dyslipidemia, glucose metabolism, and eGFR may be induced by a relative inhibition of GLUT9 or other mechanism, such as an increase in urinary UA excretion by dotinurad. However, such suggestion may be still premature because CKD is multifactorial disease and multidisciplinary treatments are required for suppression of CKD. Further studies, preferably with a great number of patients, should be performed in the future.
ABCG2 is a high-capacity UA exporter, the dysfunction of which raises hyperuricemia risk [26] (Figure 8). Dotinurad had no effect on ABCG2 [22]. However, other UA-lowering drugs, such as benzbromarone (uricosuric agent) and febuxostat (XO inhibitor), have been reported to inhibit ABCG2 completely [53]. Topiroxostat (XO inhibitor) also inhibited ABCG2 by over 80% [53]. CKD patients accumulate uremic toxins in the body. ABCG2 was a major transporter of the uremic toxin, indoxyl sulfate (IS) [54] (Figure 8). ABCG2 regulates the pathophysiological excretion of IS and strongly affects CKD survival rates [55]. High selectivity of dotinurad for URAT1 may be beneficial for suppression of progression of CKD.
Limitations of the study need to be addressed. This is a cross-sectional study, limiting inferences of causality and its direction. Although we did not change treatments for diabetes and hypertension, dyslipidemia intentionally during the study period, we cannot deny the beneficial role of the concomitant assumption of other drugs including aspect of synergism and/or the possible interaction between dotinurad and other treatments for metabolic parameters. We classified hyperuricemic patients into "UA overproduction type" and "UA underexcretion type" based on urinary UA/creatinine ≥ or <0.5, which may be weak. We should have measured 24 h urine UA, and should have analyzed urate transporter variants. To elucidate this in further studies, preferentially, RCT, that including a large number of patients, should be performed in the future.

Conclusions
Dotinurad, a selective URAT1 inhibitor, improved serum lipids, blood pressure, body weight, and albuminuria, in addition to reduction in serum UA, in CKD/DKA patients. Present study suggested that dotinurad was effective to reduce serum UA by using appropriate dose in patients with both UA underexcretion type and renal UA overload type. Furthermore, present study suggested that an increase in urinary UA excretion was favorably associated with renal function. The property of dotinurad, which selectively inhibits URAT1, but not ABCG, may be beneficially associated with pathology of CKD. URAT1 can be a therapeutic target molecule for CKD and DKD.  Informed Consent Statement: Informed consent was obtained by the opt-out approach because this study was a retrospective observational study.

Data Availability Statement:
The data supporting the findings of this study are available from the corresponding author upon reasonable request.